1. Field of the Invention
The present invention relates to a method for producing a liquid transport apparatus, the liquid transport apparatus, a method for producing a liquid droplet-jetting apparatus, and the liquid droplet-jetting apparatus.
2. Description of the Related Art
An ink-jet head, in which an ink is transported to nozzles and the ink is discharged from the nozzles to a recording medium, is known as a liquid transport apparatus for transporting a liquid to a predetermined position by applying the pressure to the liquid. Such an ink-jet head is exemplified by an ink-jet head wherein a vibration plate, which is arranged to cover a pressure chamber therewith, is deformed by means of a piezoelectric actuator to apply the pressure to the ink in the pressure chamber, and thus the ink is discharged from the nozzle communicated with the pressure chamber. For example, in the case of an ink-jet head described in Unites States Patent Application Publication No. 2005/0068376A1 (corresponding to Japanese Patent Application Laid-open No. 2005-125743), a piezoelectric layer is formed on an upper surface of a vibration plate, and an upper electrode (individual electrode) is formed at a portion of an upper surface of the piezoelectric layer overlapped with a pressure chamber. The so-called push type jetting operation is performed such that an electric potential, which is higher than that applied to the vibration plate as a lower electrode, is applied to the upper electrode, and thus the vibration plate is deformed so that the vibration plate projects toward the pressure chamber to apply the pressure to the ink in the pressure chamber, and the ink is discharged from the nozzle.
In the case of the ink-jet head described in Unites States Patent Application Publication No. 2005/0068376A1, the so-called pull type jetting operation can be also performed, in addition to the push type jetting operation as described above, such that the upper electrode is previously allowed to have an electric potential higher than the electric potential of the vibration plate to deform the vibration plate so that the vibration plate projects toward the pressure chamber beforehand, and the deformation of the vibration plate is once returned to have the original shape every time when the ink discharge request is made, after which the vibration plate is deformed again at a predetermined timing to discharge the ink from the nozzle. In the case of the pull type jetting operation as described above, the vibration plate is deformed again to project toward the pressure chamber at such a timing that the negative pressure wave, which is generated in the pressure chamber when the deformation of the vibration plate is returned to have the original shape, is reversed to the positive, and the pressure wave is overlapped therewith. Accordingly, the pressure, which is applied to the ink in the pressure chamber, can be made greater than that obtained when the push type jetting operation is performed. Therefore, the low voltage driving can be performed when the pull type jetting operation is performed as compared with when the push type jetting operation is performed.
However, in order to perform the pull type jetting operation with the ink-jet head described in Unites States Patent Application Publication No. 2005/0068376A1, it is necessary that the upper electrode should always have the electric potential higher than that of the vibration plate when the ink discharge is not performed, and the electric field should be continuously applied to the piezoelectric layer. For this reason, the following problem arises. That is, it is feared that the durability of the piezoelectric layer may be lowered, and the electric power consumption may be increased.
In the case of the ink-jet head described above, the piezoelectric layer, which is interposed between the upper electrode and the vibration plate, serves as the driving area. The vibration plate is deformed in accordance with the shrinkage of the driving area, and the pressure is applied to the ink in the pressure chamber. Areas other than the driving area are present on the piezoelectric layer, because the piezoelectric layer is formed on the entire surface of the vibration plate without providing any space. The deformation of the vibration plate is inhibited by the portions of the piezoelectric layer corresponding to the areas other than the driving area. Therefore, the following problem also arises. That is, the driving voltage is increased, and the electric power consumption is increased in order to obtain the desired deformation amount for the vibration plate during the ink discharge.